Polymers are used extensively to make a variety of products which include blown and cast films, extruded sheets, injection molded articles, foams, blow molded articles, extruded pipe, monofilaments, and nonwoven webs. Some of such polymers, such as polyolefins, are naturally hydrophobic, and for many uses this property is either a positive attribute or at least not a disadvantage. There are a number of uses for polymers, however, where their hydrophobic nature either limits their usefulness or requires some effort to modify the surface characteristics of the shaped articles made therefrom.
By way of example, polyolefins, such as polyethylene and polypropylene, are used to manufacture polymeric fabrics which are employed in the construction of such disposable absorbent articles as diapers, feminine care products, incontinence products, training pants, wipes, and the like. Such polymeric fabrics often are nonwoven webs prepared by, for example, such processes as meltblowing, coforming, and spunbonding. Frequently, such polymeric fabrics need to be wettable by water or aqueous-based liquids. Wettability can be obtained by spraying or otherwise coating (i.e., surface treating or topically treating) the fabric with a surfactant solution during or after its formation, and then drying the web.
Some of the more common topically applied surfactants are nonionic surfactants, such as polyethoxylated octylphenols and condensation products of propylene oxide with propylene glycol, by way of illustration only. These surfactants are effective in rendering normally hydrophobic polymeric fabrics water wettable. However, the surfactant is readily removed from the fabric, often after only a single exposure to an aqueous liquid. Such surfactants are effective in rendering the hydrophobic polymeric fabric wettable by lowering the surface tension of the aqueous liquid. Such a mechanism must involve at least partial removal of surfactant from the surfaces of the fibers of which the fabric is composed.
Other methods of improving wettability of polymers include methods such as corona discharge, plasma discharge, plasma jet, flame treatment, acid etching, or any method that can oxidize the surface of the substrate. However, as is known in the art, wettability introduced by these methods degenerates after treatment, as is disclosed in U.S. Pat. No. 5,700,559 to Sheu et al.
Nonwoven webs have been used to prepare a wide variety of products, including personal care products such as disposable diapers, training pants, feminine care products, baby wipes and the like. Nonwoven webs have also been used to prepare many other articles of manufacture including health care products, such as surgical drapes, surgical mask, wound dressings and the like; wipes; mops; filter materials, among many other uses.
Many of the items prepared from nonwoven webs are single use or limited use products. Most of the current nonwoven webs are prepared from polymers which are not considered biodegradable, such as polyolefins. Although currently available disposable baby diapers and other disposable products have been accepted by the public despite the fact that they are not biodegradable, these current products would benefit from improvement in the area of disposal.
Solid waste disposal is becoming an ever increasing problem throughout the world. As landfills continue to fill-up, a demand has increased for a material source reduction in disposable products. As an alternative, recyclable or biodegradable components are needed to be developed for incorporating into the disposable products. Products are needed to be developed for final disposal by means other than by incorporation into solid waste disposal facilities such as landfills.
There is a need for new materials to be used in disposable products which retain integrity and strength during use, but after such use, the materials may be disposed of more efficiently. There is a need for new materials used in the disposable product to be disposed of easily and efficiently by composting. Alternatively, the disposable product may be disposed of easily and efficiently in a liquid sewage system wherein the disposable product is capable of being degraded.
Attempts have been made to overcome some of the environmental short comings of the current disposable products by using biodegradable polymers such as aliphatic polyesters as the polymer component used to make the nonwoven web. Aliphatic polyesters, like polyolefins, are typically hydrophobic, or have a low degree of wettablility.
In addition, the use of biodegradable polymeric substrates in other applications including biomedical devices such as sutures and scaffolds for tissue regeneration has become increasingly popular. In these applications, there is a need for the biodegradable polymeric substrates to be hydrophilic and rendered hydrophilic in a manner which is safe for users of these products.
Accordingly, there is a need for a biodegradable polymeric substrate having a durable hydrophilic treatment that is stable during storage, that is biodegradable and that is wettable by water without significantly lowering the surface tension of an aqueous medium to which the coated substrate may be exposed.